Conventionally, the power converter for converting an electric power that is supplied to a motor with two sets of winding group is known in the art. For example, in a patent document, JP 2011-188674 A (Patent document 1), for the ease of distribution of heat generation to each of the winding groups, the power converter has two inverters corresponding to two sets of winding group, and the shift direction of the duty instruction signal concerning the drive of each of the inverters is switched at preset intervals.
As disclosed in the patent document 1, when the shift direction of the duty instruction signal is switched, such switching may cause a torque ripple, as well as a vibration and a sound.